Digital video can be delivered in a broadcast mode, a switched mode, or in an on-demand mode. In broadcast mode, all channels are broadcasted from a source (e.g., a cable television system hub) to all the subscribers connected to that hub (e.g., a service group). Broadcast delivery broadcasts all channels all the time, even when a channel has no active viewers. As the number of channels being broadcast increases, bandwidth demands placed on the cable television system also increase. On-demand delivery occupies bandwidth only while the viewer demands the video, and is a type of unicast delivery (i.e., to a single destination) of video assets. Switched digital video (SDV) offers improved bandwidth utilization by delivering channels with active viewers. SDV can be either switched unicast or switched multicast (i.e., any subscriber can access the channel being broadcast). Switched multicast provides the best bandwidth efficiency by not duplicating channels, while switched unicast offers the ability to personalize content.
In a traditional SDV environment (Motion Picture Experts Group (MPEG) video delivery), there are several major components: a switched digital video server; an edge QAM; a video source; and a set top box (STB) switched client. When a user selects a channel, the set top box “switched client” signals the SDV session manager of the selected channel and the service group that the set top box belongs to. If the channel is already being delivered to the service group, the SDV session manager simply returns the tuning information to the STB switched client. Otherwise, the switched digital video server will instruct the edge QAM to deliver the selected channel to the service group. The edge QAM then joins the multicast video source and delivers the video to the service group.